An electronic device can include a resistive sensor. For example, a personal electronic device with a display, such as a tablet computer, can include a strain sensor to measure the force with which a user touches the display. In another example, a home accessory, such as a security system, can include a photo-resistive sensor to measure the brightness of light within a room. Other example devices that can include a resistive sensors include cellular telephones, smart phones, personal digital assistants, laptop computers, track pads, wearable devices, health devices, sports accessory devices, peripheral input devices, and so on.
In many cases, materials selected for a resistive sensor can be affected by changes in temperature, which in turn can affect the resistance of the sensor. Thus, any local or global temperature variation within an electronic device can affect the accuracy of any calculations depending upon the determined resistance of the sensor.
In addition, the calculated resistance of a resistive sensor may be affected by power supply noise. For example, resistance can be calculated by applying a known voltage from a power supply across the terminals of a resistive sensor, measuring the current flowing therethrough, and dividing the known voltage by the measured current (Ohm's law). However, noise sources that affect the power supply can also affect the voltage output therefrom, in turn affecting the measured current, which thereafter affects the calculated resistance. Thus, power supply noise, like temperature, can affect the accuracy of any calculations depending upon determined resistance of the sensor.
In still other cases, a resistive sensor may be fabricated with multiple independent resistive strain sensors arranged in a circuit (e.g., voltage divider, Wheatstone bridge). In these examples, manufacturing variations can affect the resistance of the individual resistive strain sensors differently, which in turn can affect measurements of voltage, current, or resistance obtained from the resistive sensor.
Accordingly, there may be a present need for improved systems for measuring resistive sensors that are tolerant to manufacturing variations, power supply noise, and temperature variations.